The field of the disclosure relates generally to flight control systems and, more specifically, to a flight control module utilizing a synthetic inertial localizer deviation for detecting low-frequency instrument landing system (ILS) localizer anomalies.
Many known aircraft feature an automated landing system that controls the aircraft during landing. Automated landing systems have become increasingly more common and are frequently relied on for both instrument landings under instrument flight rules (IFR) and landings performed under visual flight rules (VFR). Known automated landing systems utilize various receivers, such as multi-mode receivers (MMRs), for example, to receive guidance signals transmitted from the ground. Such guidance signals may include, for example, ILS signals, global positioning service (GPS) landing system (GLS) signals, and/or microwave landing system (MLS) signals. The guidance signals inform the aircraft of its position relative to a desired vertical and lateral path to the runway and through roll-out after touchdown. The desired vertical path is referred to as the glideslope and the lateral path is referred to as the localizer. The glideslope is typically defined as a 3° descent with a desired intercept with the ground at 1000 feet beyond the runway threshold. The localizer guides the aircraft to the runway centerline.
The guidance signals transmitted from the ground are received by an on-board antenna and routed to redundant MMRs. Each MMR computes a localizer deviation and a glideslope deviation that are routed to a flight control module that includes the automated landing system. The localizer deviation is an indication of the aircraft's position relative to the desired path to the runway centerline. For example, the localizer deviation may indicate the aircraft is approximately 2° left of the runway centerline. The glideslope deviation is an indication of the aircraft's position relative to the desired glideslope to the runway. For example, the glideslope deviation may indicate the aircraft is 1° below the desired glideslope. The flight control module uses the localizer deviation and the glideslope deviation to command the automated landing system and to command control surfaces of the aircraft.
Under IFR conditions, the runway is typically kept clear of potential disruptions in the localizer signals transmitted from the ground. This is sometimes referred to as protecting the critical area. For example, taxiing aircraft and ground equipment are steered clear of the runway while a landing aircraft is on approach. Similarly, airborne aircraft are prohibited from flying across the airfield. In these situations, the throughput of the runway and surrounding airfield is reduced. Under VFR conditions, restrictions on operation of the runway and surrounding airfield are more relaxed, i.e., the critical area is not protected, allowing the runway and surrounding airfield to operate with greater throughput. More frequent use of automated landing systems under VFR conditions increases the likelihood of disruptions in the localizer signals transmitted from the ground. Such disruptions are referred to as anomalies in the localizer signals. Anomalies may result in drifting of the localizer input to automated landing systems, which may further result in misguiding the aircraft during landing and ultimately transitioning from automated landing to a manual landing.